Ribbed helmet



FIG. 1 is a side elevational view of a ribbed helmet showing my newdesign; the opposite side being a mirror image thereof;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof; and

FIG. 4 is a rear elevational view thereof.

The ornamental design for a ribbed helmet, substantially as shown anddescribed.